This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Expression of the myelin proteolipid protein (Plp) gene in mammals is intimately tied to the differentiation of oligodendrocytes and reaches a peak during the period in which these cells are actively myelinating the axons of neurons in the central nervous system. Low-level expression of the Plp gene has also been detected in several non-oligodendroglial cell types, including the Leydig cells of the testis, but the functional significance of this expression has yet to be determined. Several regulatory elements/regions, located within the first intron of the Plp gene, have been implicated in the spatial and temporal regulation of Plp gene expression. One of these elements, designated the antisilencer/enhancer (ASE), appears to mediate a dramatic upsurge in Plp gene expression in oligodendrocytes by counteracting the effects of negative regulatory elements located within the first intron. One possible explanation for the lower level of Plp expression in non-oligodendroglial cells is that the ASE is much less active in these cells and is relatively ineffective in counteracting the negative regulatory elements. To test this hypothesis, we analyzed the effects of a series of Plp intron 1 deletions on the expression of a linked reporter gene (lacZ) in a transiently transfected mouse Leydig cell line (TM3). The results of these experiments confirmed that the ASE element/region of Plp intron 1 has minimal activity in Leydig cells, while general and cell type specific negative regulatory elements within the intron are very active in repressing expression of the reporter gene. Preliminary evidence also suggests that a positive regulatory element located near the 5 end of the intron, and distinct from the ASE, may function specifically in Leydig cells. This issue will be explored in more depth by looking at the effects of additional deletions near the 5 end of the intron. (to start June 1, 2004)